160 . OSTEOLOGY. 
(tuberculum pharyngeum), to which the pharyngeal aponeurosis, together with the 
central part of the anterior occipito-atlantal ligament, is attached. It should be 
noted, that when the atlas is in position the pharyngeal tubercle lies in line with 
the tubercle on the anterior arch of that bone. Curving outwards and backwards 
from the pharyngeal tubercle, on either side, is an irregular ridge (crista muscularis), 
in front and behind which are attached the rectus capitis anticus major and minor 
muscles. On either side of the basioccipital, in front, there is an irregular opening 
of variable size; this is placed between the root of the pterygoid process anteriorly, 
the apex of the petrous portion of the temporal bone externally, and the outer 
edge of the basioccipital and basisphenoid internally. It is called the foramen 
lacerum medium. Opening into it in front, just external to the pterygoid tubercle, 
is the Vidian canal, whilst in correspondence with the apex of the petrous temporal 
the large orifice of the carotid canal may be seen entering it behind and from the 
outer side. In the recent condition the lower part of the foramen lacerum is 
occupied by fibro-cartilage, over the wpper surface of which the internal carotid 
artery and great superficial petrosal nerve pass to reach their respective foramina, 
whilst a small meningeal branch of the ascending pharyngeal occasionally enters 
the cranium through it. Leading outwards from the foramen lacerum in the 
direction of the alar spine of the sphenoid is the spheno-petrosal fissure, which lies 
at the bottom of the sulcus tube auditive, and disappears from view within the 
bony Eustachian canal. Passing backwards from the foramen lacerum there is a 
fissure between the outer side of the basioccipital and the posterior and inner 
border of the petrous part of the temporal bone. This, which is called the petro- 
occipital fissure (fissura petro-occipitalis) opens posteriorly into the jugular foramen. 
In the recent condition the fissure is filled up with cartilage. The under surface 
of the petrous bone included between these two fissures is rough and irregular, and 
affords attachments near its apex to two small muscles, the levator palati and the 
tensor tympani. Immediately behind the alar spine the petrous temporal is 
pierced by a circular hole, the inferior opening of the carotid canal (canalis caroticus). 
This passes upwards, and then turns inwards and forwards towards the apex of the 
bone, where it may again be seen opening into the outer and upper side of the 
foramen lacerum. Externally the wall of the vertical part of this canal is usually 
very thin, and separates it from the cavity of the tympanum, as may be seen by 
holding the skull up to the light and looking into the external auditory meatus 
(p. 116). The carotid canal transmits the internal carotid artery, together with 
the sympathetic plexus around it. It is noteworthy that the two carotid canals 
lie in line with the anterior edges of the two external auditory meatuses. 
The jugular foramen is an opening of irregular shape and size placed between 
the petrous temporal in front and the jugular process of the occipital bone 
behind. The former is excavated into a hollow called the jugular fossa, which forms — 
a roof to the upper and outer part of the space, whilst the latter, by a curved edge, 
either rounded or sharp, constitutes its posterior border. There is often considerable 
difference in the size of the jugular foramina; that on the right side (with the skull 
in its normal position) is usually the larger. The foramen is occasionally sub- 
divided into two by spicules of bone which bridge across it. Lodged within the — 
fossa is the sinus of the internal jugular vein, in front of which the inferior petrosal 
sinus passes down to join the internal jugular vein below the foramen. Effect- 
ing an exit between the two veins, in order from before backwards, are the glosso- 
pharyngeal, pneumogastric, and spinal accessory nerves. Small meningeal branches 
from the ascending pharyngeal and occipital arteries also enter the foramen. The 
two jugular foramina lie in line with a line drawn through the centres of the two 
external auditory meatuses. Following the direction of a line connecting the alar 
spine of the sphenoid and the mastoid process of the temporal, and placed immedi- _ 
ately external to the apertures of the carotid canal and jugular foramen, is the 
vaginal process of the tympanic plate of the temporal bone, the edge of which is 
sharp and thin, and serves to separate the under surface of the petrous temporal 
from the non-articular part of the glenoid fossa. Springing from this crest im- 
mediately external to the jugular fossa, and in line with the middle of the external — 
auditory meatus, is the styloid process (processus styloideum) of the temporal bone- 
